Conventional golf balls can be divided into two general types or groups: solid balls and wound balls. The difference in play characteristics resulting from these different types of construction can be quite significant.
Balls having a solid construction are generally most popular with the average recreational golfer because they provide a very durable ball while also providing maximum distance. Solid balls are generally made with a single solid core, usually made of cross-linked rubber, which is encased by a cover material. Typically the solid core is made of polybutadiene which is chemically cross-linked with zinc diacrylic and/or similar cross-linking agents and is covered by a tough, cut-proof blended cover. The cover is generally a material such as SURLYN®, which is a trademark for an ionomer resin produced by DuPont. Wound balls typically have either a solid rubber or liquid center core around which many yards of stretched elastic such as Balata or polyurethane are wound. Wound balls are generally softer and provide more spin, which enables a skilled golfer to have control over the ball's flight and final position.
Regardless of the form of the ball, players generally seek a golf ball that delivers the best combination as to maximum distance, spin and durability. Golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance for golfers at all skill levels.
The outer cover of either type golf ball are formed with various materials that may be thermoplastic urethane elastomers, Balata, ionomers (which are metallic salts of copolymer of ethylene and an acid precursor), Surlyn® blends or any other appropriate materials. The cover surfaces are formed with dimples of various numbers, sizes and patterns, which improve flight distance, control and stability. The outer surface of the ball covers usually have the manufacturers indicia disposed thereon as well as an application of a paint or clear lacquer for the purposes not only of good appearance but also of improving fight distance and protecting of the indicia imprinted thereon.
The coatings are often subject to exfoliation due to strong impact with a golf club, which not only can mar the appearance of the ball, but can adversely affect the distance and stability of the ball flight. This exfoliation can be reduced by improved adhesion techniques between golf ball cover surface and coating.
In order to improve adhesive bonding between the outer surface of the cover and the applied coating, many methods have been tried and administered. One process is the flame method. Used with golf balls this has presented a problem because of the heat generated, which can scorch the ball or cause burns to the inner polymer materials. Sand blasting is another technique for roughing up the ball, but again, this can be unsatisfactory in that precisely designed and formed dimples can be damaged. One method that has helped reduce product defects of the above nature involves treating the organic cover material of the golf ball with glow discharge plasma of unpolymerizable inorganic gas to advantageously modify the surface of the cover. A coating is then applied in an apparatus adapted to expose the all over surface of the ball to the plasma. The so-called glow plasma can be generated by applying high voltage to the gas at a low temperature of about 20° C. under a low pressure in the range of 100-200 mm Torr, more preferably 200 mm Torr. Such a method is described in U.S. Pat. No. 4,613,403 issued to Oyachi et al.
The glow discharge plasma method for treating golf balls requires the use of an apparatus that incorporates a rotating tumbler that simultaneously contains and moves a plurality of golf balls while they are being subjected to the glow discharge.
A significant problem is inherent in the make-up of conventional tumbler apparatus. Tumblers must be rigid to withstand handling thousands of golf balls per batch. They also should be designed to promote an even distribution of plasma discharge generated at about 13.56 MHz and 1200 Watts. They must allow a fast pump-down time for production efficiency. They must rotationally tumble golf balls without marking or marring them while constantly exposing the ball surfaces. A major problem with prior art tumblers is that the plurality of holes in the surfaces of these tumblers are created by a shearing process which results in holes having sharp edges on each side of sheet. The size of the holes is also of great importance as holes that are too small may severely stall the evacuation process. And holes that are too large may allow the surface of the ball to become lodged therein, whereby the ball will not move freely and thereby not receive an even coat of plasma. The holes themselves are subject to the high intensity plasma and holes that are made by the shearing method may have sharp ridges. Hole geometry of this type makes it very difficult to apply the proper anodic protective coating, and in time the plasma will erode the unprotected hole and its edges causing pitting, nicks, and other irregularities. Golf balls contacting these problem areas will be subject to marking and other potential product defects. The golf balls of the prior art are also exposed to contamination from the oil in the vacuum system. The present invention describes an apparatus that dramatically reduces, if not totally eliminates, product damage caused by these type of tumblers.